1. Field of the Invention
The present invention relates to a fixing apparatus used with an image forming system such as a laser beam printer, copying machine and the like.
2. Related Background Art
An example of a conventional fixing apparatus is shown schematically in FIG. 1.
A fixing roller 1 is formed by coating an insulative layer 3 made of fluororesin, silicone resin and the like on a rigid metallic roller, and a pressure roller 2 presses against the fixing roller 1. A recording medium which bears a toner image formed by electrophotography is passed between the fixing roller 1 and the pressure roller 2, so that the toner image is fixed onto the recording medium. Further, in the apparatus shown in FIG. 1, a DC voltage is applied between the fixing roller 1 and the pressure roller 2 so that the fixing roller contacting the toner image has the same polarity as the toner image.
In this way, an electrostatic repelling force is generated between the fixing roller and the toner image, thereby preventing the occurrence of a so-called "offset phenomenon", where the toner adheres to the fixing roller.
However, in the above-described conventional fixing apparatus, adequate insulation is not obtained, and the offset phenomenon is not completely prevented, depending upon the surface condition of the fixing roller and the material of the insulative layer.